v1.2.1 to fix `DutyCycle` and `New Period` display bugs

Releases v1.2.1

1. Fix DutyCycle bug. Check float precisison of DutyCycle only sometimes working #3
2. Fix New Period display bug. Check random dropouts #4
3. Update examples

v1.2.0 to fix `multiple-definitions` linker error, improve accuracy, DutyCycle to be optionally updated at the end current PWM period instead of immediately, etc.

Releases v1.2.0

1. Fix multiple-definitions linker error. Drop src_cpp and src_h directories
2. Improve accuracy by using float, instead of uint32_t for dutycycle. Check Change Duty Cycle #1
3. DutyCycle to be optionally updated at the end current PWM period instead of immediately. Check DutyCycle to be updated at the end current PWM period #2
4. Optimize library code by using reference-passing instead of value-passing
5. Add example multiFileProject to demo for multiple-file project
6. Update examples accordingly

v1.1.0 to add functions to modify PWM settings on-the-fly

Releases v1.1.0

1. Add functions to modify PWM settings on-the-fly
2. Add example to demo how to modify PWM settings on-the-fly

v1.0.0 to support ISR-based multi-channel PWM for Teensy boards (Teensy 2.x, Teensy LC, Teensy 3.x, Teensy 4.x, Teensy MicroMod, etc.), using Teensyduno core

Initial Releases v1.0.0

1. Initial coding to support Teensy boards, such as Teensy 2.x, Teensy LC, Teensy 3.x, Teensy 4.x, Teensy MicroMod, etc., using Teensyduno core

2. The hybrid ISR-based PWM channels can generate from very low (much less than 1Hz) to highest PWM frequencies up to 500-1000Hz with acceptable accuracy.